In recent years, balance with the global environment and reduction of the impact on the environmental have become significant goals in the industrial fields. Thus, development of products or technologies in consideration of the environment has accelerated. Such a movement is also shown in the technical field of the present invention, and particularly, an organic tin catalyst which has been widely used as a catalyst for a polythiourethane resin has been a problem in that it is harmful in human bodies due to the severity of its toxicity, environmental hormones and the like. In this regard, regulation of the use of organic tin compounds has been strengthened with advanced countries taking the lead. In the industrial field of spectacle lenses in which a polythiourethane resin is used, there has been a demand for development of a catalyst which replaces the organic tin catalyst. As a tin-free non-metal catalyst to be used for providing a general thermocurable resin, amine compounds, amine carboxylates, phosphine, and the like are known (Patent Documents 1, 2, 3, 4, and 5). Further, for use in combination with carboxylic acid metal compounds, quaternary ammonium salt compounds are known (Patent Document 6).
Furthermore, in order to prepare a polythiourethane resin as a material for a plastic lens, a cast-polymerization method is adopted in which a polymerizable composition is generally injected into a mold, and then cured by heating. In this method, a polymerization reaction is carried out while the temperature is gradually increased from a low temperature to a high temperature over several hours to several tens of hours. At that time, in order to obtain an optically homogeneous plastic lens, addition of a catalyst so as to slowly carry out a polythiourethanization reaction controlled by heat is required so that thermal inhomogeneity does not occur while raising the temperature. Furthermore, in order to sufficiently achieve resin properties including optical properties, heat resistance, and strength, it is necessary to complete the polymerization. In order to complete the polymerization, a catalyst with strong polymerization activity is used or a method for increasing the amount of a catalyst can be cited. However, such a method has a problem such that the polymerization reaction continues while the prepared polymerizable composition is injected into a mold, that is, a sufficient pot life cannot be secured. Further, there is also a problem such that during the polymerization, exothermic heat is locally generated so that it is easy for optical inhomogeneity to occur in the lenses. As a method to solve this problem, for example, a case has been reported in which the low-temperature activity is suppressed by using a Lewis acid in combination with a tertiary amine with strong activity (Patent Document 6).
Furthermore, in Patent Document 7, an internal mold release agent is described which is to be used in the preparation of a polythiourethane optical material, and which is obtained by mixing an acidic phosphoric acid ester compound and at least one kind of metal selected from the group consisting of Zn, Cu, Fe, Ga, Bi, Al, and Zr.
In Patent Document 8, dithiocarbamic acid metal salts and the like are described as non-tin catalysts for the preparation of a polythiourethane resin. In this document, it is described that such a catalyst has a catalytic activity equivalent to or higher than that of organic tin. In addition, in Patent Document 8, a catalyst is described which uses thiocarbamic acid metal salts in combination with ammonium salts. In this document, it is described that the catalytic activity of dithiocarbamic acid metal salts is improved by using it in combination with ammonium salts.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 03-084021    [Patent Document 2] Japanese Laid-Open Patent Publication No. 63-077918    [Patent Document 3] Japanese Laid-Open Patent Publication No. 62-016484    [Patent Document 4] Japanese Laid-Open Patent Publication No. 09-077850    [Patent Document 5] Japanese Laid-Open Patent Publication No. 2000-256571    [Patent Document 6] Japanese Laid-Open Patent Publication No. 2005-105084    [Patent Document 7] Pamphlet of International Publication No. 2007/105355    [Patent Document 8] Pamphlet of International Publication No. 2007/97116    [Non-Patent Document 1]“Recent Application Technology of Polyurethane”, published by CMC Publishing Co., Ltd., 1983, p. 27-31